Field of the Invention
The present invention relates to a developer suitably used for development of a photosensitive resist composition, particularly a chemically amplified positive resist composition, and to a patterning process using the same.
Description of the Related Art
As LSI advances toward higher integration and high processing speed, miniaturization of pattern rule is progressing rapidly. Especially, the expansion of the flash memory market and the increase in memory capacity lead this miniaturization. As the cutting-edge technology for miniaturization, the 65-nm node device is being mass-produced by an ArF lithography; and mass-production of the 45-nm node by an ArF immersion lithography as the next generation technology is under preparation. A candidate for the next generation 32-nm node that is under investigation includes; the immersion lithography by a super high NA lens formed of a combination of a liquid having a higher refractive index than water, a lens having a high refractive index, and a resist film having a high refractive index; a lithography by a vacuum ultraviolet (EUV) with a wavelength of 13.5 nm; and a double exposure of an ArF lithography (double patterning lithography).
A high energy beam having extremely short wavelength, such as electron beam (EB) and X-ray, is hardly absorbed into a composition such as a hydrocarbon used in a resist composition, so that a resist composition based on polyhydroxystyrene is under investigation. The resist composition for EB has been practically used for drawing a mask, but some problems recently arise in a technique for manufacturing a mask. For example, a reduction projection exposure apparatus having a reduction rate of ⅕ has been used since the age when g-beam is used as the exposure light, however, as the chip size and the diameter of the projection lens increase, the reduction rate shifts to ¼, which causes the problem that a dimensional deviation of a mask affects a dimensional change of a pattern on a wafer. In this context, it is pointed out that as a pattern becomes finer, a dimensional deviation on a wafer tends to be larger than a dimensional deviation of a mask; and thus, Mask Error Enhancement Factor (MEEF) is calculated from a dimensional change of a mask as the denominator and a dimensional change on a wafer as the numerator. In a 45-nm pattern, MEEF often exceeds 4. When the reduction rate is ¼ and MEEF is 4, accuracy equivalent to an unmagnified mask is substantially required for mask production.
As to the exposure apparatus for mask production, an exposure apparatus using laser beam or EB has been used to enhance line-width accuracy. Moreover, increasing the acceleration voltage of an electron beam gun enables further miniaturization; and thus, the acceleration voltage has been increased from 10 keV to 30 keV, and 50 keV with the recent main stream, and further study of 100 keV is taking place.
Note that, deterioration in sensitivity of the resist film is becoming a problem as the acceleration voltage is increased. As the acceleration voltage is increased, the forward scattering effect within the resist film becomes smaller, so that contrast of the electron beam drawing energy is enhanced thereby leading to improvement in resolution and size controllability, while sensitivity of the resist film is deteriorated because the electron passes through the resist film with free draining condition. In the exposure apparatus for mask production, direct drawing is done by way of a one-stroke sketch, so that the deterioration in sensitivity of the resist film causes the decrease in productivity; and thus, this is not desirable. Accordingly, a resist film with higher sensitivity is required, and investigation of a chemically amplified resist composition is getting underway.
In addition, with the miniaturization of a pattern of the EB lithography for mask production, thinning of the resist film is progressing in order to prevent pattern collapse during development due to a high aspect ratio. In the photolithography, thinning of the resist film significantly contributes to enhancement of the resolution. This is because a device became more flattened by introduction of CMP and others. In mask production, a substrate is flat, so that film thickness of the resist film formed on the substrate to be processed (e.g., Cr, MoSi, and SiC2) is determined on the basis of the light shielding rate and the phase difference control. To make the film thinner, dry etching resistance of the resist film needs to be enhanced.
Generally, it is said that there is a relationship between the carbon density and the dry etching resistance of the resist film. In the EB drawing, which is not influenced by absorption, the resist composition based on a novolac polymer having a high etching resistance has been developed. An indene copolymer shown in Patent Document 1 and an acenaphthylene copolymer shown in Patent Document 2 not only have high carbon density but also show an enhanced etching resistance by rigid main chain structures due to the cycloolefin structures.
It has been reported that a soft X-ray exposure having a wavelength of 5 to 20 nm (EUV) is less absorbed by carbon atoms. The increase of carbon density is effective to enhance not only the dry etching resistance but also the transmittance at the range of the soft X-ray wavelength.
With the progress of pattern miniaturization, there arise the problem of blur of the figure due to acid diffusion. For ensuring the resolution of a fine pattern with a dimensional size of 45 nm or less, the control of acid diffusion is important besides the enhancement of the dissolution contrast, which has been conventionally suggested. However, in a chemically amplified resist composition, sensitivity and contrast are increased by acid diffusion, so that if the acid diffusion is extremely controlled by reducing the post exposure bake (PEB) temperature and time, the sensitivity and the contrast are significantly decreased. There is a close relationship between the kind of an acid-labile group and the acid diffusion distance, and thus, it is desired to develop an acid-labile group that advances the deprotection reaction at an extremely short acid diffusion distance.
On the other hand, the trade-off relationship has been reported among the sensitivity, edge roughness, and resolution. When the sensitivity is increased, the edge roughness and the resolution are deteriorated, and when acid diffusion is controlled, the edge roughness and the sensitivity are decreased although the resolution is enhanced. With regard to this, addition of an acid generator capable of generating bulky acid is effective to control acid diffusion, but the control of acid diffusion leads to the reduction in edge roughness and sensitivity, as mentioned above. Thus, it has been suggested to copolymerize the polymer with an acid generator of an onium salt having a polymerizable olefin. Patent Documents 3 to 5 describe a sulfonium salt and an iodonium salt having a polymerizable olefin, capable of generating a specific sulfonic acid. The photoresist using a base polymer copolymerized with a polymerizable acid generator can reduce edge roughness and simultaneously enhance both properties of resolution and edge roughness since acid diffusion is small and the acid generator is uniformly dispersed into the polymer.
Moreover, the EUV lithography has severe problems of pattern collapse and bridge defect. These problems are supposed to be caused by swelling of the resist film in a developer. To reduce the swell in an aqueous tetramethylammonium hydroxide (TMAH) solution, a developer of an aqueous tetrabutylammonium hydroxide (TBAH) solution has been investigated, but it is still inadequate for a pattern formation of 20 nm or less. Therefore, it has been desired to develop a further developer that can prevent swelling.